1. Technical Field
The invention relates to a patterned substrate, an electro-optical device, and a method for manufacturing an electro-optical device.
2. Related Art
Known displays equipped with light emitting elements include organic electroluminescence displays (organic EL displays) used as an electro-optical device equipped with an organic electroluminescence element (organic EL element).
Methods for manufacturing organic EL elements are generally classified by the kind of material that makes up its organic EL layer thereof. When the material that makes up the organic EL layer is a low-molecular weight organic material, a vapor phase process is utilized, in which the organic EL layer is formed by the vapor deposition of this low-molecular weight organic material. On the other hand, when the material that makes up the organic EL layer is a high-molecular weight organic material, a liquid phase process is utilized, in which the high-molecular weight organic material is dissolved in an organic solvent or the like, and a coating of this solution is applied and dried.
With an inkjet method, which is a type of liquid phase process, tiny droplets of solution are discharged, so the location where the organic EL layer is formed, the film thickness, and the like can be controlled more precisely than with other liquid phase processes (such as spin coating). Furthermore, since an inkjet method involves discharging the droplets only in the region where the organic EL layer is to be formed (the element formation region), the high-molecular weight organic material (the raw material) can be used in a smaller amount.
With an inkjet method, however, as the contact angle of the droplets increases with respect to the element formation region (that is, as wettability decreases), the discharged droplets end up clumping in just one part of the pattern formation region. As a result, depending on the boundary between droplets and other factors, this can lead to problems such as a loss of uniformity of shape (such as the film thickness uniformity of the organic EL layer, or the film thickness uniformity between organic EL layers).
In view of this, it has been proposed in the past that the wettability of the discharged droplets be improved in an inkjet method (see JP-A-2002-334782, for example). In JP-A-2002-334782, the pattern formation region (over the transparent electrode) is subjected to a lyophilic plasma treatment (oxygen plasma treatment) before the droplets are discharged. This improves the wettability of the droplets and increases the uniformity of the pattern shape within the pattern formation region.
In general, an organic EL layer is formed from a laminated pattern having at least a light emitting layer that emits colored light and a hole transport layer formed between this light emitting layer and an anode (such as an ITO film). When a laminated pattern such as this is formed, with an inkjet method, the upper layer pattern and the lower layer pattern are made of materials with different polarity in order to prevent the lower layer pattern from dissolving into the droplets that form the upper layer pattern. For example, the upper layer pattern is formed by dissolving or dispersing a lipophilic light emitting material in an aromatic organic solvent, and the lower layer pattern is formed by dissolving or dispersing a hydrophilic hole transport layer in water.
In other words, a material with low wettability with respect to the lower layer pattern is selected for the material that forms the upper layer pattern. Accordingly, the lower layer pattern has to be subjected to the above-mentioned lyophilic plasma treatment in order to ensure the wettability of the droplets that form the upper layer pattern.
However, since the lower layer pattern (such as a hole transport layer) is formed from an organic substance with low plasma resistance, a problem is that subjecting this lower layer pattern to a plasma treatment or the like can damage the lower layer pattern. Another problem is that tacking on this plasma treatment step results in correspondingly lower productivity of the organic EL display.